This invention relates to apparatus used in the maintenance of large aircraft propeller assemblies.
The propeller assemblies used in present-day military transport and civilian aircraft are vested with a significant degree of engine and flight condition accommodating ability. It is common practice, for example, to provide such propellers with the ability to vary the blade pitch position in response to engine rotational velocity, aircraft flight needs, and; of course; to provide for complete reversal of the blade pitch and the propeller generated thrust force during landing or other ground maneuvering operations. In large multiple-engine aircraft, the control of propeller blade pitch angle also involves considerations of pitch and rotational synchronization between multiple propellers. The determination of blade operating pitches in such larger aircraft of the type used by the U.S. military is frequently accomplished through the use of pressurized hydraulic systems and for reasons involving reliability and engine-propeller design convenience, the hydraulic system of such propellers is frequently arranged to be self-contained within the propeller assembly as opposed to being a part of either the aircraft or the engine hydraulic systems.
In the case of military turbine engine driven propellers, for example, the propeller hydraulic system includes a plurality of pressure generating and scavenge pumps which are connected in a redundant or failure-preventing backup arrangement and are energized by a combination of engine torque and electrical motor driven--frequency an electrical motor of the three-phase 400 cycle alternating current variety. In this hydraulic system arrangement, the electric motor driven, pressure generating and scavenge pumps are identified as auxiliary pumps to the engine driven pumps. These electrically driven auxiliary pumps, in addition enable the changing of propeller blade pitch angles even though the propeller is rotationally at rest, that is, during an in-flight feathered propeller condition or in conjunction with an engine start-up in-flight or for ground static blade angle changing. As described below, these auxiliary pumps are also useful during the latter phases of a propeller maintenance routine.
The complexitY of the final adjustment and check-out operations to be performed on such propeller assemblies can be appreciated from a cursory review of the technical order document which describes the performance of such steps for a military aircraft. The technical order identified as TO-1C-130B-2-11, for example applies to the herein referred-to propeller assembly of the C-130 aircraft. This document has been periodically updated, most recently in August of 1988. The contents of the TO-1C-130B-2-11 technical order are hereby incorporated by reference in the present document. Section two of this technical order is of special interest with respect to the present invention, since it recites in some detail a number of the check-out and adjustment operations which are supported by the apparatus of the present invention.
It is parenthetically notable in this section two that the blade pitch angle in a propeller of the described type should not be changed when the propeller has been exposed to temperatures of 32.degree. F. or lower without first warming the propeller hub oil through the use of warm air or engine running. This precaution is required in order that damage to the propeller blade shank seals and consequential hydraulic system oil leakage may be avoided. In practice, however, this warmup procedure requires about 1/2 hour of maintenance personnel time to accomplish. Both this time delay and the difficulty of working on the propeller assembly in unpleasant outdoor weather conditions are largely avoided by use of the present invention and result in an engine and propeller assembly that are operationally verified while yet indoors.
Periodic maintenance, including complete teardown and component inspection, are therefore normal activities in the life cycle of most aircraft components, including variable pitch propeller assemblies. In the latter phases of this maintenance activity, it is usually desirable to reintegrate the components of the propeller assembly and then mount this assembly on the propeller driving shaft of an engine gearbox while the engine is held in a portable test stand. In this condition it is possible to perform a number of visual and functional checks of the propeller assembly in a more convenient and non-aircraft mounted condition. Such off-aircraft inspection and testing of a worked-upon propeller assembly is found to be of great convenience in an operational aircraft situation for a number of additional very practical reasons. Such inspection and testing, for example, provides a significantly improved probability of the propeller assembly being in defect-free usable condition before investment of airframe time into the maintenance procedure.
The ability to perform a major number of check-out steps on a reassembled propeller assembly within the aircraft hanger or propeller shop as opposed to performing these steps after the reassembled propeller is mounted on the aircraft can also be understood to minimize the hours that maintenance personnel are required to work around the aircraft and out-of-doors in hostile weather conditions. Avoiding the physical height, awkward positioning and large physical separations between cooperating maintenance team members needed when these check-out steps are performed on the aircraft is itself a significant improvement in the propeller maintenance sequence. When final propeller check-out is performed on the aircraft, for example, it is frequently necessary to position one maintenance team member in the cockpit while another team member is located close by the propeller assembly to perform leak checking, adjustments, and propeller function verifying activities.
In order to accomplish these final check-out and basic functioning activities while the propeller assembly is indoors and mounted on the output shaft of an engine gearbox assembly, it is necessary to achieve a propeller assembly cooperative apparatus which provides both propeller assembly component energization and propeller control signals together with indication of proper functioning of the sensor apparatus that is included within the propeller assembly. Preferably, these energy source, control signal; and sensor indication functions should originate in an apparatus that is convenient and suited for use in the aircraft maintenance environment--apparatus that provides both maximum maintenance person convenience and realistic interfacing with the signal and energy ports of the propeller assembly. The present invention involves apparatus fulfilling these objectives.
Apparatus for testing aircraft propellers is known in the patent art and is exemplified, for example, by the patents of H.O. Hem, U.S. Pat. No. 2,201,369, and E. Martin et al, U.S. Pat. No. 2,343,383, wherein unmounted aircraft propellers are tested and repaired with respect to their static and dynamic balance.